This invention relates to a method for separating and recovering protein and isoflavones from a plant material containing protein and isoflavones, and more particularly to a method of using ion exchange to separate and recover protein and isoflavones from a plant material.
Plant proteins provide an important source of nutrition worldwide. For example, soybeans are an excellent source of nutrition for both humans and animals. Soy protein is commercially extracted from soybeans to provide an inexpensive, highly nutritious source of protein. An isolated soy protein can be utilized in numerous dietary applications for both its nutritional benefits as well as functional characteristics the protein lends to a food or beverage. Some common foods in which soy protein is used include ground meats, emulsified meats, and marinated meats; beverages such as nutritional beverages, sports beverages, protein fortified beverages, juices, milk, milk alternatives, and weight loss beverages; cheeses such as hard and soft cheeses, cream cheese, and cottage cheese; frozen desserts such as ice cream, ice milk, low fat frozen desserts, and non-dairy frozen desserts; yogurts; soups; puddings; bakery products; salad dressings; and dips and spreads such as mayonnaise and chip dips.
Certain plants such as soybeans, peas, beans, and other legumes contain isoflavones as well as protein. Isoflavones are phytoestrogenic compounds which have been found to provide humans with a variety of health benefits. For example, the isoflavones present in soy are genistein, daidzein, glycitein, formononetin, shown in FIG. 1, and their natural glycosides and glycoside conjugates, shown in FIG. 2. As used herein, xe2x80x9cMalxe2x80x9d is defined as xe2x80x9cmalonylxe2x80x9d and xe2x80x9cAcxe2x80x9d is defined as xe2x80x9cacetylxe2x80x9d. Another biologically active isoflavone found in plants other than soy is biochanin A, shown in FIG. 1.
The health benefits associated with these isoflavones are numerous, and continue to be discovered. For example, some of these isoflavones have been found to inhibit the development of breast and prostate cancers, and to induce apoptosis in breast and prostate cancer cells. Isoflavones extracted from soy have also been found to inhibit the development of atherosclerosis, to lower the blood serum concentration of total cholesterol and low density lipoprotein cholesterol, to reduce or prevent menopausal symptoms, to inhibit the development of Alzheimer""s disease, and to inhibit bone loss due to osteoporosis.
Isoflavones have been associated with the bitter, beany taste of legumes which contain significant amounts of the compounds. Accordingly, it is desirable to separate and recover both an isoflavone-depleted, pleasant-tasting protein material and the health-beneficiary isoflavones from a plant material containing isoflavones and protein.
Methods are known in the art for separating isoflavones from a plant material containing protein and isoflavones. For example, U.S. Pat. No. 5,679,806 provides a process for extracting, isolating, and purifying isoflavones from a plant material in which the plant material is extracted with an alcohol solvent to extract the isoflavones from the plant material; the alcohol extract containing the isoflavones is adsorbed onto a reverse phase matrix followed by specific desorption of the isoflavones from the matrix by a step grade elution, where the isoflavones are crystallized from the recovered eluent. Japanese Patent No. 1-258669 provides a process in which soybeans are soaked in warm water to convert isoflavones to their aglycone form; the aglycone isoflavones are then reflux-extracted from the soy material with an aqueous alcohol; the extracted liquid is condensed and dried; the dried material is dissolved in alcohol and adhered to a reverse-phase resin; and the isoflavones are eluted from the resin with an aqueous alcohol.
These methods, while satisfactory for separating and purifying isoflavones from a plant material, do not provide a method for recovering a purified protein material and isoflavones from a plant material containing both isoflavones and protein. Both methods utilize an alcohol solvent to extract the isoflavones from the plant material. Plant proteins such as soy protein are substantially insoluble in alcohol solutions, and will be left as a byproduct residue from the alcohol extraction, along with other plant materials insoluble in alcohol such as plant fiber materials.
U.S. Pat. No. 4,428,876 (the ""xe2x80x9c876 patentxe2x80x9d) provides a process for separating both plant proteins and flavanoids, including isoflavones, from a plant material containing flavanoids and protein. A plant material is extracted with an aqueous alkaline solution to form an extract containing the flavanoids and protein, and the extract is separated from unextractable and insoluble plant materials. The extract is applied on a non-polar or slightly polar adsorbent resin as it is, or after being acidified, to adsorb the flavanoids on the resin. Acidification causes the protein to be precipitated from the extract. If acidified, the precipitated protein is separated from the extract prior to application of the extract on the resin. After applying the extract on the resin, the resin is eluted with water and the eluent is collected to provide an eluent containing carbohydrates, and, if the extract was not acidified, protein. The water eluent is acidified to precipitate and separate the protein if the protein was not precipitated and separated from the extract prior to application on the resin. The flavanoids are then separated from the resin by eluting the resin with a polar solvent such as methanol or ethanol and collecting and concentrating the eluent.
Utilizing the process of the ""876 patent, isoflavones and carbohydrates/protein are not separated cleanly due to the nature of the isoflavones, and the resin and eluents used in the process. As shown in FIGS. 1 and 2, isoflavones are relatively polar compounds, particularly in their natural glycoside or glycoside conjugate forms. Due to their polar nature, the isoflavones adsorb weakly to the non-polar or slightly polar resin. In an aqueous environment, the protein and carbohydrates are also relatively polar compounds which do not bind particularly strongly to the resin. Therefore, adsorbtion of the isoflavones, carbohydrates, and proteins to the resin, itself, is not effective to provide good separation of the compounds upon elution of the resin with a solvent since the compounds are easily displaced from the resin, and are not particularly differentiated from each other by interactions with the resin.
The process of the ""876 patent will provide separation of some of the isoflavones from the protein and carbohydrates due to the relative solubility of the isoflavones in the eluent. For example, if the eluent initially used is water, and the extract is an extract of soy (which contains the isoflavones genistein and daidzin, among others), genistein will be sparingly eluted with protein and carbohydrates since genistein is only slightly soluble in water, however, daidzin will be eluted with the protein and carbohydrates since daidzin is soluble in water.
What is needed, therefore, is an effective, commercially viable process for cleanly separating and recovering protein and isoflavones from a plant material containing the same.
The invention provides an improved method of separating and collecting isoflavones and protein from a plant material which can be efficiently and economically performed on a commercial scale. The method involves separating and collecting isoflavones and a plant protein by contacting a clarified plant protein extract containing isoflavones and protein with a polar ion exchange resin; allowing the isoflavones to bind with the polar ion exchange resin; separating and recovering an isoflavone depleted protein extract from the ion exchange resin; and separating and recovering the isoflavones from the ion exchange resin. In a preferred embodiment, the separated and recovered isoflavones are converted to their aglucone form.